1. Field of the Disclosure
This disclosure relates generally to systems and methods for depositing a material on a substrate, such as a printed circuit board, and more particularly to an apparatus and systems and methods for inspecting such deposits.
2. Discussion of the Related Art
There are several types of prior art material application systems used for depositing assembly materials, such as solder, for a variety of applications.
One such application uses a stencil printer to print solder paste onto a circuit board. In a typical surface-mount circuit board manufacturing operation, a stencil printer is used to print solder paste or some other material onto the circuit board, which has a pattern of pads or some other conductive surface onto which solder paste will be deposited. The circuit board is automatically fed into the stencil printer and one or more small holes or marks on the circuit board, called fiducials, is used to properly align the circuit board with the stencil or screen of the stencil printer prior to the printing of solder paste onto the circuit board. Once the circuit board has been properly aligned with the stencil in the printer, the circuit board is raised to the stencil, solder paste is dispensed onto the stencil, and a wiper blade (or squeegee) traverses the stencil to force the solder paste through apertures formed in the stencil and onto the board. As the wiper blade is moved across the stencil, the solder paste tends to roll in front of the blade, which desirably causes mixing and shearing of the solder paste so as to attain desired viscosity to facilitate filling of the apertures in the screen or stencil. The solder paste is typically dispensed onto the stencil from a standard cartridge. In other embodiments, a pressurized head may be provided to dispense solder paste to apertures in the stencil.
Another such application in the assembly of integrated circuit chips and other electronic components onto circuit board substrates uses automated dispensing systems for dispensing very small precise amounts, as dots or continuous lines, of viscous material onto a circuit board. The viscous material may include liquid epoxy or solder paste, or some other related assembly material.
In both of the aforementioned systems, it is common that after such material is deposited onto a circuit board, an imaging system is employed to take images of areas of the circuit board for, in certain instances, the purpose of inspecting the accuracy of the deposit of material on the circuit board. Another application of the imaging system involves the aforementioned aligning of the stencil and the circuit board prior to printing in order to register the openings of the stencil with the electronic pads of the circuit board. One such imaging system is disclosed in U.S. Pat. No. 7,458,318 to Prince, which is owned by a subsidiary of the assignee of the present disclosure.
One challenge facing the design of such stencil printers and dispensing systems is the ability to perform a fast, comprehensive inspection of a large area of a substrate after the disposition of solder paste in a single pass. Further, while methods have been developed to perform consistent two-dimensional modeling of solder paste on a substrate, e.g., the circuit board, through existing area-scan and line-scan formats, such approaches are limited various ways. In typical practice, both area-scan and line-scan formats have a limited field of view as a result of the relatively short distance between the lens of the imaging system and the substrate. For example, in area-scan format, imaging a large area may require substantial time as the imaging system moves point-to-point to acquire a large area of a substrate. Likewise, line-scan format may require multiple passes to acquire a large area.